|Each tile in the middle of the room has a pit and piston underneath it. First it drops, igniting the tunnel, and then slams up to the ceiling.
A DC 14 Wisdom (Perception) check reveals that the tiles 10′ into the room have a couple of mm of space between it and the next tile. This area is as wide as the room and 20 ft deep.
When one of these tiles is stepped on, the tile immediately drops 20 feet. A creature on the tile must make a DC 14 Dexterity saving throw or take 1d6 falling damage.
When the piston hits the bottom, the pit fills with flame as an explosion drives the piston up again. Creatures in the pit take 3d6 fire damage, with a DC 16 Dexterity saving throw for half damage.
The piston drives all the way to the ceiling. Creatures on the piston may make a DC 14 Dexterity saving throw when it leaves the pit to jump off. Otherwise, the creature takes 3d6 bludgeoning damage when the piston reaches the top.
The piston then resets.
Note that if a creature jumps to an adjacent tile that has a piston, this cycle is repeated.
The trap can only be disabled from underneath the tile. A creature must get under the tile, requiring a DC 14 Acrobatics check to get under the tile while it is rising. The creature still takes 2d6 falling damage unless mitigated somehow. If the creature moves at any rate slower than normal falling speed, they will take 2d6 bludgeoning damage as the piston lands on top of them at the bottom, as there is only 3′ of clearance. Once underneath, a DC 16 Dexterity check with thieves’ tools will cause the piston to rise where it can be stopped and locked at any point.
Creatures may also try to hop from one tile to another by making successive Dexterity saving throws from tile to tile. Once a creature is aware of the trap, these saving throws have advantage.